It is well known in the art to protect electrical loads connected to a vehicle electrical system by means of fuses and circuit breakers. In the event of malfunction of a load, such as an electrical short, the load or a group of loads allocated to a particular circuit will be disconnected from the electrical system as the fuse or circuit breaker supplying power to the circuit opens. Power will remain disconnected from the circuit until the fault is removed and the open fuse is replaced or the circuit breaker is reset.
In addition, certain loads are equipped with individual overcurrent protection and/or individual cut-off devices that utilize a self-checking or self-diagnostic routine that either runs continuously, at timed intervals, or is initiated by the occurrence of an internal or external event. If a fault is detected, the load disconnects itself from the vehicle electrical system in accordance with an internal control, such as a microprocessor or a microcontroller, and a set of predetermined instructions such as a computer program.
Alternatively, a fault in a load or a group of loads can also be detected by an external means, such as with a supervisory control module. If a fault is detected, the supervisory control module typically does not directly disconnect the load. Instead, the supervisory control module issues a command to the internal control of the faulty load instructing the control to disconnect the load. The cut-off of the load is then accomplished independently by the internal control for the load or circuit found to be faulty.
There are several disadvantages associated with relying on a load to disconnect itself. For example, if the malfunction in the load affects the load's control, the load may be unable to disconnect. In addition, faults external to the load, such as shorted wiring, often cannot be resolved by disconnecting the load.
Another shortcoming of current means for protecting loads is that they typically do not consider the system-level impact of disconnecting a load. In fact, some loads are critical to the proper operation of a system. For example, a vehicle steer-by-wire system such as the system disclosed by Byers et al. in U.S. Pat. App. No. 2002/0107621 utilizes a plurality of actuators, sensors and controls to transmit steering commands from a hand wheel to the steering system of the vehicle. In addition, a hand wheel actuator configured to receive commands from the hand wheel system is utilized to provide the driver with tactile feedback regarding road conditions. If such a system were to be equipped with individual circuit protection devices, such as fuses and circuit breakers, a momentary electrical overload of a load, such as an actuator, could result in a loss of at least a portion of the vehicle's steering function.
There is a need for a way to protect loads that is not subject to malfunctions in the load and also protects the vehicle wiring. There is a further need for a way to control loads without needlessly crippling or disabling critical components of a system.